The invention is in the field of short-arc high-intensity gas discharge lamps, such as are used in certain photographic projectors. It is common practice to manufacture integral lamp and reflector combinations employing such a type of lamp.
A typical short-arc high-intensity discharge lamp comprises a quartz envelope having a thick-wall bulb-like arc chamber, and a pair of elongated electrodes are sealed into the envelope at opposite ends and along a common axis. The envelope includes elongated stems extending along and around portions of the electrodes. The arc length between the inner ends of the electrodes is about 2 or 3 millimeters, and the overall bulb diameter is about 8 to 10 millimeters, and overall length (including stems) is about 5 centimeters, for a 300-watt metal halide gas lamp. Thus, this short-arc lamp has an arc length of less than half the outer bulb diameter. U.S. Pat. No. 3,379,868 to Taillon discloses a short-arc lamp mounted in a reflector laterally of the projected light's optical axis, and U.S. Pat. No. 3,700,881 to Slomski discloses a short-arc lamp mounted in a reflector along the optical axis. U.S. Pat. No. 3,780,342 to Grimshaw et al discloses a ballast circuit for a short-arc lamp, which applies a relatively high starting voltage pulse to the lamp electrodes, followed by a relatively lower operating voltage.